1. Field of the Invention
This invention relates to magnetic bubble domain devices. In particular, a FIFO magnetic bubble domain shift register for use in a memory and having continuous data storage capabilities.
2. Description of Prior Art
Many magnetic bubble domain devices are-known in the art. Such magnetic bubble domain devices are arranged to provide various systems and system applications. Most appropriate for magnetic bubble domain systems appears to be memory applications. Typically, memory applications utilize shift registers and the like.
In memory shift register designs, there have been proposed many simple loop first-in, first-out (FIFO) bubble domain memory shift registers and the like. These shift register designs usually include three basic control functions, i.e. generation, annihilation and detection of the bubbles. However, in the existing circuits, various problems are encountered. For example, when the detection circuit is inserted into the storage loop, there is produced a finite separation of time and distance between the detector and the annihilator positions. Of course, the generator can be located in a separate branch and, thus, positioned independently and, therefore, aligned with respect to one or more of the other control functions. If the generator is aligned with the annihilator, a gap of time and space in the memory loop is produced. This requires a chip align mode of operation in a multiple chip system. If the generator is aligned with the detector, there is a delay between the generator and annihilator which requires additional electronics to keep track of the status and operating mode of the chip.
On the other hand, if the detector is merely removed from the propagation track or storage loop wherein the position thereof can be aligned with the generator and annihilator simultaneously, obvious advantages can be obtained. However, this arrangement typically requires a replicator to replicate any incoming bubble so that a bubble may be supplied to the detector and, as well, propagated through the storage loop track to provide nondestructive readout. Existing active replicators can be used for this purpose but, generally, require bipolar control pulses wherein complicated driver circuitry is required. In the situation where a passive replicator is utilized, the requirement for control currents is obviated but bubbles are continuously replicated wherein the detector is prevented from operating in an alternate bit read mode. This latter shortcoming places restrictions on the operation and design of the detector. Moreover, the detector operation is then a serious limitation on the operation of the bubble domain system due to the inherent operating characteristics of the detector and associated materials.